Many biological agents and toxins have been determined to have the potential to pose a severe threat to both human and animal health, to plant health, or to animal and plant products. An attenuated strain of a select agent or an inactive form of a select toxin may be excluded from the requirements of the Select Agent Regulations.

Various agencies have contributed to the list of select agents, and as such groups of agents and toxins have been made primarily related to whether it causes harm in humans, animals, both, and/or plants.